Have you ever considered that at any given moment you're probably breathing in someone else's fart?
Think about it. If you're in an elevator with someone who farts, you're bound to do it.
If you're in a room with several people and one of them farts, you're going to do it.
If you're in a building with a hundred people and ten of them fart, it's inevitable.
In a world full of billions of people, each of them farting in an enclosed atmosphere... well, you're pretty much stuck doing it.
How's it feel? Does it feel good?